This invention relates to compositions and methods for imparting stain resistance to polyamide fibers using carbonated solutions containing dye-resist agents made up of condensation products of sulfonated phenols or naphthols and formaldehyde, with or without the presence of added fluorochemicals. More particularly, this invention relates to compositions and methods for (1) regenerating the stain resistant properties of previously treated polyamide fibers and (2) imparting stain resistant properties to polyamide fibers which have not been previously treated with stain resistant chemicals.
The term "stain resistant" as used in the industry means the ability of a polyamide fiber to resist staining when subjected to Food, Drug and Cosmetic Red Dye No. 40 (hereinafter called Red Dye 40). Fibers of polyamides (including natural polyamides such as wool and silk and synthetic polyamides most commonly referred to as nylons) may be woven into carpets and other textile materials which are long wearing and relatively inexpensive. They may be dyed into a variety of colors but tend to become permanently stained when subjected to most artificial colorants normally added to foods, beverages, medicines, cosmetics and the like, and also by chromophores found in most fruits and fruit based drinks, including wines. It is a well known fact that most nylon and wool carpeting is replaced because of staining and not because the carpet is worn.
It has been known for some time that polyamide fibers, which contain free amino groups, can be made stain resistant by applying sulfonated naphthol- or phenol-formaldehyde condensation products which react with the free amino groups forming an ionic bond. These sulfonated condensation products, commonly called "dye-resist agents", are well known in the art and are described in detail in U.S. Pat. Nos. 4,592,940; 4,501,591 and 4,699,812. Typical of these sulfonated naphtholic or phenolic condensation products are those available under the tradenames Wilnostain.RTM. (U.S. Polymeric), Erionol.RTM. NW and Erionol.RTM. PA (Ciba-Geigy), Intratex.RTM. N (Crompton and Knowles), and Misitol.RTM. NBS (Mobay). These and similar products have been sold for several years in the textile trade for use as dye-resist agents or agents to improve wetfastness and are recommended for use at an acidic pH of about 4 to 6. These dye-resist condensation products can be thought of as "colorless dyes" that bind to the free amino dye sites on polyamide fibers so that these sites are not available for reaction with dyes such as Red Dye 40, fruit stains, and similar materials.
The dye-resist products are normally applied to polyamide fabrics, such as carpeting, at the time they are manufactured but have not been well applied to installed carpets or fabrics subsequent to the manufacturing process. Two factors have been largely responsible in preventing the application of stain resistant chemicals to installed polyamide carpeting. The first factor is that, when improperly applied, these materials tend to yellow upon exposure to environmental conditions, such as the presence of NO.sub.2, which is commonly found in the atmosphere. This causes obvious problems, especially on light dye shade fabrics. The second factor is that the normally high pH of cleaning solutions tends to prevent bonding of the stain resistant materials to the free amino groups of the polyamides and increases the yellowing tendency of these sulfonated condensation products.
Stain resistant carpets have been available only since about 1986 and are primarily made of one of the nylons, e.g. nylon 6 (polycaprolactam), nylon 66 (polyhexamethylene adipamide), nylon 11 (polymer of 11-amino undecanoic acid) and others. Carpets installed prior to that time are not stain resistant. It has been conventional practice to coat non-stain resistant fibers with a fluorochemical to prevent wetting of the fiber surface by both oils (hydrophobic) and aqueous (hydrophilic) solutions and minimize contact between the carpet and soiling materials. However, fluorochemicals offer little protection against staining unless the staining substance is immediately removed from the carpet before it has a chance to react with the polyamide fibers. The treatment of textiles with fluorochemical polymers is illustrated by U.S. Pat. Nos. 3,574,791; 3,728,151; 3,816,167; 3,916,053; 4,043,923; 4,043,964; 4,160,777; 4,192,754; 4,209,610; 4,264,484; 4,317,736; 4,604,316; 4,681,790 and 4,695,497. These fluorochemicals are commonly referred to under the tradenames Scotchgard.RTM. (Minnesota Mining and Manufacturing Co.), Teflon.RTM. (DuPont), Zonyl.RTM. (DuPont), Zepel.RTM. (DuPont), MPD 5737 and MPD 6202 (DuPont).
The durability of dye-resist agents and fluorochemicals on polyamide fibers varies greatly. Physical wearing caused by foot traffic on the carpet, abrasive action between fibers and sand or other particulate matter deposited on the carpet, and the like cause some removal of dye-resist agents even through they are chemically bonded to the fibers. Also fluorochemicals, which form a polymeric coating, are also removed over a period of time. Cleaning of the carpet with alkaline cleaning solutions also causes some chemical removal of dye-resist agents and fluorochemicals. Thus, over a period of time, carpets which once were treated to resist stains or resist oil and water solutions are made vulnerable to staining. Even more alarming is the vulnerability of carpet fibers which have never been treated to any type of dye-resist protection, even though they may have been previously treated with fluorochemicals.
It would therefore be desirable to provide a method for regenerating stain resistant polyamide fibers and making non-stain resistant polyamide fibers resistant to stains. However, as previously stated, there has heretofore been no convenient method for treating installed carpeting for such purposes. The dye-resist chemicals must be applied at an acid pH in order for the free amino groups on the polyamide fibers to become protonated and react with sulfonate anions of the dye-resist condensation products. Moreover, in order to have a truly stain resistant carpet, the free amino groups (--NH.sub.2) of all fibers, from the nap to the base, must be protonated (--NH.sub.3 .sup.+) and reacted with sulfonate ions (--SO.sub.3 .sup.-). This is generally done by treating the fibers prior to being woven into a carpet or by submersing the carpet in an acid solution containing the dye-resist agents. The fibers or carpet made of fibers, as the case may be, may then also be immersed in a rinse or neutralizing solution to bring the pH to about neutral followed by drying. A neutral pH is important in that if the acid were to remain on the fibers it could, in the presence of moisture, result in the hydrolysis of the polyamide chain creating more free amino groups as new dye sites rendering the fiber non-stain resistant. The presence of acids can also cause gradual fading of some dyestuffs. Moreover, a neutral fiber is necessary for the safety of those who come into contact with the fibers.
If an acid solution of a dye-resist agent is applied to an installed carpet it is difficult to insure that the fibers are completely contacted by the solution to react with all dye binding sites. Also, it is difficult, if not impossible to rinse the fibers to a neutral pH. One way of doing this would be to subject the fibers to an alkaline treatment, with or without the presence of a detergent. However, any use of an alkaline agent immediately removes some of the dye-resist agent. Also, if the fibers have been treated simultaneously with a fluorochemical, some of the fluorochemical will be removed unless it has first been completely dried prior to the rinsing treatment.